Presence but not synthesis of thyrotrophin-releasing hormone in rat salivary glands detected by radioimmunoassay and northern blot analysis.

Thyrotrophin-releasing hormone (TRH) is one of the ubiquitous peptides first isolated from hypothalamus. This study sought to examine if it could also be detected in rat submandibular salivary glands, as can other neurogastrointestinal peptides. Radioimmunoassay of submandibular gland homogenates revealed TRH-like immunoreactivity in all samples from male rats (637.34 pg/gland +/- 166.17, n = 15). In contrast, Northern blot analysis to determine whether the peptide was locally synthesized in the glands failed to detect TRH mRNA. Consequently, the presence of TRH in the glands (as revealed by radioimmunoassay) could be associated with binding to presumptive TRH receptors in the mediation of physiological activities.